The present invention relates generally to a seat reclining apparatus, and more particularly to a seat reclining apparatus of a round type that has a round speed-reduction mechanism comprising an internal gear, and an external gear having a smaller number of teeth than the internal gear, where the external gear rotates with respect to the internal gear in meshing contact with the internal gear.
In recent years, there are proposed and developed round-type seat reclining apparatuses for automotive vehicle with a round differential mechanism through which a seatback is rotated by means of an electric motor with a high gear ratio. Japanese Published Patent Application No. 2000-166679 and French Published Patent Application No. 2759333 show such round-type seat reclining apparatuses that comprise a base plate secured to a seatcushion arm, an internal gear secured to a seatback arm, an external gear secured to the base plate and meshed with the internal gear where the number of teeth of the external gear is one or two smaller than that of the internal gear, an eccentric drive mechanism that rotates the external gear with respect to the internal gear so that the meshing site therebetween moves circumferentially, and a holder ring that binds and supports the base plate, the external gear, and the internal gear. On the other hand, Japanese Published Patent Application No. 2004-229951 shows a structure for eliminating a play between the internal gear and the external gear, where the structure includes a pair of wedge members which is employed with a spring member and a center shaft to eccentrically drive the external gear in meshing contact with the internal gear.